Green sensitization of photographic silver halide emulsions



July 19, 1960 J. E. JONES 2,945,763

GREEN SEINSITIZATION OF PHOTOGRAPHIC SILVER HALIDE EMULSIONS Filed June 19, 195s i Fig.

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NAHTHOTHMZOL//VE F ig. 2

REF/.www5 E JEAN E l0/VES INVENTOR.

fw/4% MW A 7' TOR/VEYS Unite This invention relates to photography, and more particularly, to a method for altering the sensitivityV of greensensitized photographic silver halide emulsions.`

It has long been known that benzimidazolocarbocyanine dyes are useful in sensitizing photographic silver halide Y emulsions to the green region of the spectrum, i.e.,` that portion of the-spectrum lying between aboutV 50Oand, 60'() ma. These dyes have been of particular interestras greensensitizers, andl in particular, in the emulsions intended for use in color photography,V since they aregenera-lly characterized by very sharp absorption. Dyes of this type have been previously described inthe technical and patent literature. See, for example, Ogata Proceedings of the Imperial Academy (Tokyo), v ol. 9 (1933), page- 602,. Among the most useful of the benzimidazolocarbocyanine dyes are those containing one or more chlorine atoms substituted on the benzene ring of the benzimidazole nucleus. Y

However, many of these benzimidazolocarbocyanine dyes suffer from the disadvantage that their maximum absorptions are so deep that there is considerable diliiculty in'colorl reproduction, especially thereproduction of orange colors whose reliectance is changing rapidly: with wavelengths in the region of the maximum'y absorptions of these dyes,r which is about 575mg. j

I` have now found a novel" means of hypsochromically shifting the absorptions of these useful dyes, andiin many instances, in providing superseneitizing` effectsvv witlr these dyes at the same time. Y Y

It is, therefore, an` object of my invention to. provide an improved means of sensitizing photographic silver halide emulsions to the green region of the spectrum. Another object is to produce photographie silver halide', emulsions having improved green, sensitivity.k Still, an: other object is to provide photographic silver-halide emulsions which have been supersensitized bya combination of! the above-mentioned sensitizing dyes' with4 certain heterocyclic compoundsv as hereinafter defined.

Other objects will become apparent fron- 1- a considera,V

sensitizing dyes include those representedlby the followingV general formula:

i nl/ \n wherein R andv R1k each represents and alkyl group; suchV asmethyl, ethyl, Ilit-hydroxyethyl, n-propyl', nbutyl', ,tt-r'zar box-yethyl, y-carboxypropyl, (or 4,).l-carboxylhutyl", )9s-sulfoethyl, y-sullfoinopyL` `i-sulfelmtyl.,v fsulfebutyl, etc.

rates Patent O `ice 2 Y (e, .g., an alkyl group` ycontaining from 1 to 4; carbon atoms), R2 and R3 each represents an alkyl group, such as methyl, ethyl, n-propyl, n-butyl, etcte-a,` an alkyl erreur containing from 1 to 4 carbon atoms.) Aor, an aryl group, such as phenyl, o, mor p-tolyl, etc. (e.g., amononiiclear aromatic group of the benzene Series), d and 1 1 each.rep-4 resents a positive integer of from l to- 3 and X, represents an acid radical, such as chloride, bromide, iodide, benzenesulfonate, p-toluenesulfonate, methylsulfate ethylsulfate,

perchlorate, etc. As indicated above, the dyes, such as those illustrated by `Formula I above,v which are par=4 ticularly useful in color photography, comprise those dyes containing one or more chlorine atoms substituted on the Vbenzene ring of the benzimidazole nucleus. Where either R or R1 of Formula I represents acid-substituted alkyl groups, such as a sulfoalkyl group, the dyes are generally regarded as anhydro dyes, and, a particularly useful group of such dyes can be represented by the following general formula:

wherein R has the values given above, and`D represents an alkylenel group, such as'ethyl'ene, trimethylene, tetra- Y methylene, ymethyltrimethylene, etc. Another.' group of dyes embraced by Formula I which are particularly useful in my invention can be representedby the following general formula:

ethyl, n-propyl, n-butyl, etc. (e.g., an alkyl group containing from 1 to 4 carbon atoms) 4 R5rrepresents an alkyl group, such as methyl, ethyl, etc. (e.g., an alkyl group containing from l to 2 carbon atoms), or an aryl group, such as phenyl, o, mor p-tolyl (e.gl, a' mononuclear aromatic, group, of the benzene series), Q; represents an oxygen atom or an arylimino group, such as phenylimino, tolylimino, chlorophenylimino, etc. (e.g., a mononuclear arylimino group), and Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus of the naphthothiazoline series or the naphthoselenazoline series. The carbocyclicY rings ofthe nuclei defined by Z above can contain inert substituents, such as alkyl groups (e.g., methyl, ethyl, etc.), alkoXy groups (e.g., methoXyl, ethoxyl, etc.), etc.

The benzimidaaelecarbocyanine; dyesY ofl my: invention,

containing a sulfoalkyl group on at least one of the nitrogen atoms, can be prepared according to the methods described in copending applications, Serial No. 680,003, led August 23, 1957, in 4thenames of 1. E. Jones and I. Spence, now patent No. 2,912,329, granted November 10, 1959, and Serial No. 698,324, filed November 25,V

1957, in the names of L. G. S. Brooker and G. H.Keyes,

now U.S. Patent 2,917,516, granted December 15., 1959... Certain of the benzimidazolocarbocyanine dyesuseful in practicing my invention are also described in Van Lare U.S. Patent 12,739,149, issued March 20, 1956.

' Typical of the compounds embraced -by Formula II are the following:

1-methy1-2-proptony1methylene--naphthothtazoline 1-ethyl-2- (Z-phenyllmlnopropyltdene) --naphthothlazollne 1-ethy1-2- [2- (p-tolylimino) propylidene] --naphthothiazoline 2-acetonylidene-iethyl--naphthothiazoline 1-methyl-2-benzoylmethylene--naphthothiazollne CHS - 2-acetonylldene-l-methyl--naphthoselenazoline 1) 1 2-benzoylmethyle1re-s-etnyl-mphthouimmm i CH3 2-acetonylidene-S-methyl-a-naphthothiazoline The heterocyclic bases of my invention represented by Formula II above have also been described in the prior art. The compounds of Formula II, wherein Q represents Il C-:CH-C-CHS an oxygen atom, can be prepared according to the method described in Brooker et al. U.S. Patent 2,112,139, issued March 22, 1938. The compounds of Formula II, wherein Q represents an arylimino group, can be prepared as described in Brooker et al. U.S. Patent 2,298,732, issued October 13, 1942.

Many of the compounds represented by Formula II- above are colorless and have an absorption maximum lying outside of the visible region of the spectrum. It

was, therefore, unexpected to find that these compounds e sensitizing effect.

alone. This elect has been compared previously to synergism, which is sometimes encountered in other branches of chemistry. I have further found that the degree of hypsochromic shift in the absorption ofthe benzimidazolocarbocyanine dyes can be controlled to some extent by the amount of the compound of Formula II which is added. Of course, addition of increased quantities of the compoundrof Formula II will produce an increased shift in absorption up to a point which varies from dye to dye and addition vof further quantities of the compounds of Formula II beyond that point does not produce a corresponding shift in the absorption characteristics. The optimum amount of the compound of Formula II employed in my invention can vary, depending upon-the effect desired. The most advantageous amounts of the sensitizing dye and the compound of Formula II can be determined by running a series of test emulsions wherein various quantities of either ingredient are employed. In general, the amount of sensitizing dye used can vary rather widely and I have found that from about 5 to about 200 mg. per mole of silver halide are quite adequate. The amount of compound of Formula II can likewise be varied, as described above, and I have found that from about 10V to about 200 mg. per mole of silver halide of the compounds of Formula II are quite adequate. VThe ratio of the amount of sensitizing dye to the compound of Formula II can likewise be varied, and I have found that, in general, this ratio can vary from about 1:5 to about 5:1 (by. weight). TheI 5 thereof, the emulsions can then be digested for a short period of time prior to coating on a suitable support, such asv glass, cellulose derivative iilm, metal, paper, polyvinyl .acetal film, etc. After coating to a suitable thickness, the film can then be allowed to dry.

My invention is primarily directed to the ordinarily employed gelatino-silvenhalide developing-out emulsions, e.g., gelatino-silver-chloride, -chlorobromide, -chloroiodide, -chlorobromiodide, bromide and -bromiodide developing-out emulsions. While the results inthe following table were obtained using gelatino-silver-bromiodide emulsions, 'excellent vresults have 4also been obtained using gelatino-silver-chlorobromide emulsions. Emulsions which form the latentrimage mostly inside the silver halide grains, such as theI emulsions set forth in E. B.- Knott et al. U.S. Patent 2,456,956, dated December 21, V194,8, lcan also be employed in practicing my 'invention.

Photographic silver halide emulsions, such as those listed above, containing the sensitizing combinations of my invention can also contain such addenda eis-chemical sensitizers, eg., sulfur sensitizers (eg, allyl thiocarbamide, thiourea, allylisothiocyanate, cystine, -etc.), various gold compounds (e.g., potassium chloroaurate, auric trichloride, etc.) (see U.S. Patents W. D. Baldsiefen 2,540,085, granted February 6, 1951; R. E. Damschroder 2,597,856, granted May 27, 1952 and H. C. Yutzy et al. 2,597,915, granted May 27, 1952), various palladium compounds, such as palladium chloride (W. D. Baldsiefen U.S. 2,540,086, granted February 6, 1951), potassium chloropalladate (R. E. Stauier et al. U.S. 2,598,- 079, granted May 27, 1952),` etc., or `mixtures-of such sensitizers; antifoggants,` such as ammonium chloroplatinate (A. P. H. Trivelli et al. U.S. 2,566,245, granted August 28, 1951), ammonium chloroplatinite (A. P. H. Trivelli et al. U.S. 2,566,263, granted August 2,8, 1951), benzotriazole, nitrobenzimidazole, -nitroindazole, benzidine, mercaptans, etc. (see Mees, The Theory of the Photographic Process, Macmillan Pub., 1942, page 460), or mixtures thereof; hardeners, such as formaldehyde (A. Miller U.S. 1,763,533, .granted June 10, 1930),

of the same batch of photographic gelatino-.slver-,brom iodide emulsion were added (1) a benzimidazolocarbocyanine dye of the type illustrated in Formula I or Ia or Ib and (2) a combination of a benzimidazolocarhocyanine dye'and aheteroeyclic base of the type illustrated in Formula Il. Before coating, the emulsions containing the addenda were digested for a short time in a tank maintained at 5 0-52" C. The different portions of emulsion were then coated on conventional supports and eX- posed in the usual manner in an Eastman Type Ib Sen- A,sitometer through a Wratten No. 12 filter, i.e., a filter which transmits only light having a Wavelength greater than 495 mit, and in a spectrograph. The exposed coatings were then developed for 3 minutes (except in Exl amples 4-7, development was for 4 minutes) in a developer having the following composition:

, Gra-ms N-methyl-paminophenolsulfate 2.0 Hydroquinone 8.0 Sodium sulte (anhydrous) 90.0 Sodium carbonate (.monohydrate) 52.5 Potassium bromide 5.0

Water to make one liter.

No data showing the sensitometric properties of the Compounds 0f Formula il alone are given, since it has been found that these derivatives have little or `no sensitizingaction of. their own on the emulsions used'. Dierent emulsions were used in some of the examples, although tlteemulsions in eacn individual example were obtained from the same batch. in Table A, the coatings of Exf ,amples Al.-3 wereohtained from the same batch of .unsensitizedemulsiom the coatings of Examples 4-7 were obtained from the same batch of unsensitized emulsion and #the eoatings of `Examples Y8-.10 were obtained from the same .hatch .of unsensitized emulsion. The emulsions y used in Examples 4-7 .hada speed somewhat higher than thatof the emulsions used in Examples 1,-3. The minus blue reiative speeds (i.e., .the speedgof Vthe .unsensitized .emulsion being set at 100 for purposes of comparison), gamma, jfog and absorption maximum (X maximum) Afor .each ofthe coatings are given in the vfolltwving table:

chrome alum (1,763,533), .glyoxal (I. Brunken .U.S. 1,870,354, granted August 9, 19.32), dibromacrolein (0. Block etal. Br. 406,750, accepted March 8, .1934), etc.; color couplers, .such as those described ,in I. F. Salminen et al. U.S. Patent 2,423,730, -granted .Tuly 7 1947, Spence and Carroll U.S. Patent` 2,640,776, Aissued June 2, 1953., etc.; or mixtures yof such addenda. Dispersing agents gfor color couplers, 4such asrthose set forth in U.S. patents E. Jelley et al. 2,322,027, granted .Tune .15, 1943, `and L. D. Mannes etaL 2,304,940, granted :December 15, 1942 can also be employed in `the above-described emulsions. Y

AThefollowingexamples"will serve to illustrate the :man Der lot practicing my invention; lTo -diierent portions In Table A above, the .sensitizing dyes used contained Vchlorine substituents on the benzene ring of the .ben-

zimidazole nucleus. However., it .is .not essential that these dyes lhavenhlorine .substituents ,in every instance, `although it has been found that .the chlorine-substituted dyes are quite outstanding .in their properties.I Benecial effects have .also been obtained wherein `the benzimidazolocarbof cyanine dyes of my invention contained .no ISub..s ittlents, or contained .substituents other than chlorine, such as bromine, acetyl, ethylcarhamyl, ',methyl, ethyl, etc., attached to the benzene ring of the benzimidazole nuclei. lha-vealso found that the .benecial effects `of my invention can Vbie-.obtainedv using lunsymmetrical .benzimidazole dyesflize, dyes wherein Aone of the benzimidazole nuclei 7 has been replaced by a diierent basic nucleus, such as benzoxazole, benzothiazole, etc. In general, my invention has been found to be most useful wherein the sensitizing dye is a symmetrical benzimidazolocarbocyanine dye, i.e.,

l a shift of from 575 me to 550 me occurs when using a compound of Formula 1I.

It has also'been found that various hemicyanine. dyes,

dyes wherein the benzimidazole nuclei are identical inso- 5 dide can be employed in combination with the benzifar as substituents on the nitrogen atoms and on the midazolocarbocyanine dyes of my invention, so that useful benzene ring are concerned. In the following table, the supersensitizing effects can be obtained. For example, results were obtained in exactly the manner described combining the afore-mentioned hemicyanine dye with above with respect to the coatings of Table A. The Dye (a) of Table A, produced a 275% increase in speed, emulsion used was a conventional gelatino-silver-bromioalthough there was a shift in absorption of only from dide emulsion and the coatings were prepared as de- 576 to 572 mp.. i scribed for Table A. Exposure and development were As indicated above, many of the benzimidazolocarboidentical to that of Table A, the time of development cyanine dyes of my invention can be prepared according being about 4 minutes for each of the exposed coatings. to methods previously described in the prior art. The The speed, gamma andfog, together with absorption 15 following examples will serve to illustrate the preparamaximum for each of the coatings are given in the foltion of several dyes useful in practicing my invention, as lowing table: well Yas intermediates necessary for the preparation of TABLE B Minus Blue Exposure Example Addenda (gJmol. AgX) Rel. Gamma Fog A Speed Max.

(o) 5,5'diehloro1,1',3,3-tetraethylbenzimidazolocarbocya- Y 11 nine iodide (.08) 100 1. 7 .0s 575 (p) dye (o) compound 2 (.065) 135 2. 5 .09 565 (q) 1,1'dinbuty15,5,6,6tetraehloro3,3diethylbenzimid- 12 azolocarbocyanine iodide .08) 166 2.8 .08 580 (r) dye (q) (.08) plus compound 2 (.065) 186 2. 8 .08 58D (s) 5,5,6,6tetrachloro3,3diethyl1,1'dip ny enzimldaf 13 zolocarbocyanine iodide (.08) 148 2.8 08 585 1 (t) dye (s) (.08) plus compound 2 (.065) 145 2. 9 .08 570 (v) dye (u) (.08) plus compound 3 (.005) 178 3.1 .O7 575 (z) dye (w) (.08) plus compound 3 (.065) 165 2.8 .07 575 (y) anhydro 1,1' dicarboxyethyl- 6,6' diametro-3,3 diethyl- 16 benzimidazolocarbocyanine hydroxide (.08) 20 .6 .07 575 (z) dye (y) (.08) plus compound 4 (.065) 107 2.2 .07 570 17 bocyaune iodide (0.08 155 2. 5 07 580 (b) dye (a') (.08) plus compound 3 (.065) 186 2. 6 08 570 (c') 1,1-(6dicarboxyethyl)4,5,4',5tetrachloro3,3'diethyli 18 benzimidazolocarbocyanine iodide (.08) 25 3. 1 07 590 (d) dye (c) (.08) plus compound 1 (.065) 125 3. 1 07 580 (f) dye (e) (.08) plus compound 1 (.065).....' 57 3.1 .07 540 (a')1,1,3,3tetraethylbenzimidazoloearbocyanine iodide 2o .0s 11 .a .0s 530,560

(h') dye (g') (.08) piuscompound 2 (.065) 3o 2.2 .2o 525, 56o 21 (i') dye (0') (.08) plus compound 3 (.065) 25 2.4 .11 525 My invention can be further described with reference to the accompanying drawings which are diagrammatic reproductions of the reflectance curvesfor several of the coatings of the examples in Table A.

In Fig. 1, curve A represents the reectance (percent) for a processed ordinary gelatino-silver-bromiodide emulsion containing anhydro-5,5,6,6 tetrachlorol,ldiethyl 3,3'di(3su1fobutyl)benzimidazolocarbocyanine hydroxide, while curve B represents the reectancef (percent) of the sensitized emulsion illustrated by curve A, butA to which 3-ethyl-2-(2-phenylimino-propylidene)--naphthoi thiazoline had been added. The sensitometric properties of these coatings are illustrated in Examples 6 and 7 above.

In Fig. 2, curve C represents the reilectance (percent) of a processed ordinary gelatino-silver-bromiodide emulsion containing 5,5',6,6tetrach1oro1,l,3,3'tetraethyl benzimidazolocarbocyanine iodide, while curve D represents the reectance (percent) of the emulsion represented by curve C, to which 1-methyl-2benzoylmethylene l-naphthothiazoline had been added. The sensitometric .properties of these coatings yare shown in Examples 4 and 5 above.

' It can be seen by reference to Fig. 1 that a shift in absorption from 578 ma to about 556 m/.r occurs upon addition of a compound of Formula II, while in Fig. 2,

aol

these dyes. It will beV seen by reference to these examples that my invention contemplates benzimidazolocarbocyanine dyes containing two chlorine atoms on a single benzene ring of the benzimidazole nucleus, regardless of their position on the ring. It is to be understood that my invention also contemplates benzimidazolocarbocyanine dyes containing no substituents on the benzene ring of the benzimidazole nucleus.

The reaction mixture was chilled and the solid filtered ol and then it was suspended in 60 ml. of water containing 2 g. of sodium iodide. After chilling for two hours, the crude dye was iiltered olf. The dye was suspended in 60% methyl alcohol and the suspension was heated to boiling and then cooled. After ltering, the dye was suspended in 60 ml. of methylV alcohol, cooled and tiltered. The dye was obtained as brownish crystals in a A6% yield, M.P. 205-206 C. with decomposition.

4bromovaleric acid (1.8 g., 2 mols.) and 5,6-dichloro- 1ethyl-2-methylbenzimidazole (4.6 g., 2 mols.{l00% eX- cess) were heated together on a steam bath for four hours. A solution of sodium ethoxide (0.58 g. of sodium in 50 ml. lof -absolute ethyl alcohol) was added -to the `quarternary salt, the mixture was reuxed forten minutes and cooled. Then chloral (0.74 g., 1 mol.) was added and the resulting mixture was reuxed for one hour. The reaction mixture was chilled and the solid filtered off and then it was suspended in 60 ml. of water containing 2 g. of sodium iodide. After standing for two hours, the crude dye was tiltered off. The' dye was dissolved in 400 ml. of 70% -methyl alcohol and one ml. of triethylamine, the solution was filtered and the filtrate made acid with glacial acetic acid. The pure dye was obtained as brownish-orange crystals in a 5% yield, M.P. 256 257 C. with decomposition.

Anhydro 4,5 dichloro-3-ethyl-2-methyl-1-(4-sulfobutyl)benzimidazolium hydroxide (3.65 g., 2 mols.) and chloral (0.74 g., 1 mol.) were added to a solution of sodium ethoxide (;58 g. of sodium in 60 m1. of absolute ethyl alcohol), and the reaction mixture was refluxed for one hour. The mixture was chilled, the solid was filtered off and the residue was suspended in 60 ml. of water containing g. of sodium iodide. After chilling, the crude dye was filtered r01T. The dye was suspended in 100ml, of `hot methyl alcohol, the suspension was `cooled and iiItered. The dye was obtained as reddish crystals VAin a 25% yield, M.P. 294-295 C. with dei composition. f

' (4-Sulfobuty'l)-benzimidazolium hydroxide 6,"7-Dic`hloro-'1-ethyl-2-methylbenzimidazole (23,2 Vg.) an-d 1,-4-butane sultone (13.6 g.) were heated together at 17'0' -C. The temperature increased to 210 C. and solid separated. The mixture wasV heated at 150 C. `for one hour. VThe solid was crushed and washed with acetone. The yieldof cream crystals was 32 g.

To a suspension of 252 g. (1 mol.) of crude 5,6-dichloro-N-ethyl-Z-nitroaniline in 2400 ml. of water 4and 20 ml. of concentrated hydrochloric acid "at 70 C. was added 246 g. (3 mol.+33% excess) of iron powder in small portions and with vigorous stirring. The reaction mixture was stirred for an additional four hours at 75- '85 C. A lte'r-aid was added and the suspended solid ltered off. The solid and liquid fractions were extracted lseparately with chloroform. Therchloroform extracts were combined andthe solvent removed on a steam bath. To the cooled residue was added, with shaking, 200 ml. of .acetic anhydride. The acetic acid and excess acetic anhydride were distilled off slowly until the internal temperature finally reached 200'J C. The residue was lextracted with 3% hydrochloric acid and the extract was made alkalineV with sodium hydroxide. extracted with ether. The ether solution was dried over solid potassium hydroxide. After filtering, the ltrate was concentrated and the residue was fractionated. The base was obtained ,as a colorless oil in a 40% yield, 5B1. 1162-167.C./1 mm.

Y 1 lio 430ml, of e707@` solutionef ethylamine inV vwater was added 229 g. (1 mol.) of 2,3,4trichloronitrobenzene in small portions with stirring. Most of the solid dis- The base was -solved and the solution became warm. It was cooled in an ice-water bath and then allowed to stand at room temperature overnight. The reaction mixture was diluted with 2 l. of water, filtered, and the solid washed with water and air dried for 24 hours. The crude damp produce was used without further purification. A 2 g. sample was recrystallized from ethyl alcohol and 1.8 g. of bright orange needles were obtained, M.P. 50-53 C.

Unsymmetrical benzimidazolocarbocyanine dyes useful'in my invention can be prepared as described in Gevaert Belgian Patent 532,735, vgranted November 13, 1954.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it Will be understood that variations and modifications can be edected within the spirit and scope of the inventio-n as Vdescribed hereinabove and 4as defined in the appended claims.

What I claim as my invention and desire secured by Letters Patent of the United States is:

1. A photographic silver-halide emulsion containing (l) a sensitizing dye selected from those represented by the following general formula:

' and R3 each represents a member selected from the group consisting of an'alkyl group and an aryl group, d'and n each represents a positive integer of from 1 to 3, and. X represents an acid radical, and (2) afcompound selected from those represented by the .following general formula.: l

wherein R4 represents an alkyl group, R5 represents a member selected from the group consisting of an alkyl Vgroup and an aryl group, Q represents a member vselected sions.V sIonre wherein Di represents an alkylene group, and (2) a compound selected from those represented by the following general formula:

wherein R4 represents an alkyl group, R5 represents a member selected from the group consisting of an alkyl group and anlaryl group, Q represents a member selected from the group consisting of an oxygen atom and an arylimino group, and Z represents the non-metallic ato-ms climas 11 e necessary to complete a heterocyclic nucleus selected from the group consisting of those of the naphthothiazoline series and those of the naphthoselenazoline series.

3. A photographic silver halide emulsion containing (1) a symmetrical sensitizing dye selected from those represented by the following general formula:

wherein R and R1 each represents an alkyl group and X represents an acid radical, and (2) a compound selected from those represented by the following general formula: Y

wherein R4 represents an alkyl group, R5 represents a member selected from the group consisting of an alkyl group and an aryl group, Q represents a member selected from the group consisting of an oxygen atom and an arylimino group, and Z represents the nonmetallic atom's necessary to complete a heterocyclic nucleus selected from the group consisting of those of the naphthothiazoline series and those of the naphthoselenazoline series.

4. A phoptographic silver bromiodide emulsion .containing (1) a sensitizing dye selected from those represented by the following general formula:

Rg R1 if i \C=CH-CH=CH-C/ I \N/ wherein R and R1 each represents an alkyl group, R2 and R3 each represents a member selected from the group consisting of an alkyl group and an aryl group, d and n each represents a positive integer of from 1 to 3, and X represents an acid radical, and (2) a compound selected from those represented bythe following general formula:

wherein R4' represents an alkyl group, R5 represents a member selected from the group consisting of an alkyl group and an aryl group, Q represents a member selected from the group consisting of an oxygen' atom and an arylimino group, and Z represents the nonmetallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of those ofthe naphthothiazoline series and those of the naphthoselenazoline series.

5. A photographic silver halide emulsion containing 1) a symmetrical sensitizing dye selected from those represented by the following general formula:

wherein D represents an alkylene group, and (2) a compound selected from those represented by the following general` formula:

wherein R4 represents an alkyl group, R5 represents a member selected from the group consisting of an alkyl group and an aryl group, Q represents a member selected from the `group consisting of an oxygen atom and an arylimino group, and Z represents the non-metallic atoms necessary to complete a' heterocyclic nucleus selected vfrom the group consisting of those of the naphthothiazoline series and those of the naphthoselenazoline series.

' 6. A photographicsilver bromiodide emulsion containing (l) a symmetrical sensitizing dye selected from those represented by the following general formula:

,t i .wx wherein R and R1 each represents an alkyl group and X represents an acid radical, and (2) a compound selected from those represented by the following general formula: /,Z\\ 4 R4-N- o=onc|z=q R5 wherein R4 represents an alkyl group, R5 represents a member selected from the group consisting of an alkyl groupand an aryl group, Q represents a member selected 'from thegroup consisting of an oxygen atom and an arylimino group, and Z represents the non-metallic atoms ,necessary/to Vcompletev a heterocyclic nucleus selected References Cited in the le of this patent UNITED STATES PATENTS f 2,1 12,139

Brooker et al ...L Mar. 22, 1938 2,298,732 Brooker et al. Oct. 13, 1942 2,694,638 Carroll Nov. 16, 1954 2,739,149 Van Lare Mar. 20, 1956 ,2,778,823` Brooker et al. Ian. 22, 1957 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING (1) A SENSITIZING DYE SELECTED FROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 